[Bug target/62233] unnecessary shift instructions to prepare loop counter

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62233

Oleg Endo <olegendo at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|powerpc64le                 |powerpc64le sh*-*-*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-09-25
                 CC|                            |olegendo at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #2 from Oleg Endo <olegendo at gcc dot gnu.org> ---
On SH, the original code above looks OK (no extra shifts generated), however,
changing it to:

void clear2 (S* s )
{
   int i;
   int len = s->l;

   int* p = s->b;
   for (i = 0; i < len; i++)
       p[i] = 0;
}

results in:
        mov.l   @r4,r1
        cmp/pl  r1
        bf/s    .L13
        add     #4,r4    <<<<
        shll2   r1       <<<<
        add     #-4,r1   <<<<
        shlr2   r1       <<<<
        mov     #0,r2
        add     #1,r1
    .align 2
.L10:
        mov.l   r2,@r4
        dt      r1
        bf/s    .L10
        add     #4,r4
.L13:
        rts    
        nop

This looks very similar to what is happening in PR 55190.
BTW, compiling the two functions with -O3 results in a detected memset, while
at -O2 a memset is not detected.